Acoustic indicator for directional receivers



Jan. 27, 1948.l D. A. QUARLE'S ACOUSTIC INDICATOR FOR DIRECTIONALREQEIVERS Filed April 19, 1944 lll MR *Ill MSS N @Fx INI/EN T 0R By o.A. QUA/nfs WM ATTORNEY Patented Jan. 27, 1948 N g 1 2434957"UNi'rEosTATEs PATENT OFFICEI ACOUSTIC INDICATOR FOR DIRECTIONALRECEIVERS Donald A. Quarles, Englewood, N. J., assgnor to Bell TelephoneLaboratories,

Incorporated,

New York, N. Y., a corporation of New York Application April 19, 1944,Serial No. 531,704

lective receiver toward a source of .incomingI waves. In systems ofdirection iinding and object location,v it is common to use conicalscanning' "or two-dimensional lobe switching in association with acathode ray display device as a means for the precise determination ofthe direction of a source of radiant energy or of a reilecting object.There have also been suggested certain acoustic indicating means formaking such determinations. to an improved acoustic indicator for usewith conical or other cyclic scanning systems or with lobe switchingsystems. Deviation from correct pointing of the receiving antenna in thesystem of the invention is indicated by an amplitude modulation orvariation in the amplitude of the response of the acoustic system overthe scanning or switching cycle. The variations in response give rise tocharacteristic rhythms'a particular rhythm being correlated with a,deviation in a particular direction. In a preferred embodiment of theinvention, the acoustic response is interruptedto form a series ofpulses, for example, a -group, of four, separated by a silent interval.Other numbers of pulses per group may be employed, if desired, or theacoustic'response may be more or less continuous. Incorrect pointing isindicated by a rhythmical rise and fall in the acoustic intensity. Somedevice such as the introductionrof the recurring silent interval may beemployed to enable the observer to associate the accent of the rhythm orthe accented pulse as the case may bewith a particular portion, forexample, quadrant, of thescanning motion. The position of the accentindicates the quadrant in which the maximum signal is received and thisinformation enables the operator to correct the pointing ofthe'receiving antenna until all pulses are received in equal intensity,indicating that the axis of the scanning receiver is accurately directedtowards the radiation source.

In the drawing,

. Fig. 1 is a Vschematic representation of a preferred'embodiment of theinvention;

Fig. 2 is, a. graphical representation of the acoustic response in thesystem cf Fig. 1, when the'receiving antennais ,accurately pointed to-Ward the, source of radiation;

Figs. 3 and 4 are graphical representations of the acoustic response ofthe system when incorreotly pointed; and Fig. 5 shows an alternativecircuit arrangement which may be substituted, for the portion of thesystem of Fig. 1 Vshown within a dot-dash line.

In Fig. 1, a directonally selective arrange- The present invention isdirected 8 Claims. (Cl. 250-7-11) lsistance as a function of itstemperature.

2v ment AIll for receiving and detecting radiant energy is illustratedas comprising a paraboloidal reector II and an eccentrically mounted,rotatable thermistor or bolometer I5 which may be rotated by a motor I3through a, shaft Y I4. By a thermistor is meant a resistor whichexhibits a marked or material variation in re- The thermistor I5preferably rotates in the focalplane of the reflector II, which planeislocated as infdicated in the drawing by a dot-dash line 3|. The rotationof 'the thermistor I5 serves to effect conical scanning in a mannersimilar to a' more a wave of single frequency is received, in which.

case the thermistor may beplaced at a point in the tuning system wherethe heating eiect is a maximum. 1 l

' Let it firstl be assumed that radiation ,is being received from thedirection'lof the axis. o-f the shaft I4, that is, that the receiving,arrangement I Il is correctly pointed in the direction of the incomingwaves. Rotation ,of the, thermistor' l5 along withV the shaft I4 thencauses noffluctuation in the .intensity ofthe radiant energy reflectedto the thermistor I5 by the reflectonfll, as will be evident from therotationalA symmetry of the system through which the energy is trans'-mitted to the thermistor. The thermistor in this case is irradiated byradiant energy of Aunvarying intensity and maintains aconstant-'resistance substantially unaffected bythe rotation. l Theelectrical circuit of the thermistor; I5 will now be traced, beginningwith a lead I6 preferably connecting one terminal of the thermistor withthe conductive material. of the shaftl4, which shaft may be composedpartly orwholly. of metal. The other-terminal of the thermistorisconnected by an insulated lead .I1-which ir'ireferably passes throughthe interiorof the shaft |4 and is in turn connected-to a-ivslipring.I-8..J.A brush I 9 is maintained infconstant'contact with the slip ringI8. Thebrush I9 is connected by a lead 20 to la series circuitcomprising a .source material of the shaft I4.-4 One ofthe interruptersis shown as comprising a preferably narrow .con- A tactor 23' bearingupon a commutator. 23 having four conductive segments all connectedconduc- 3 tively with the conductive portion of the shaft I4 andseparated atthe .periphery -of the Vcommutator by insulating :segmentsThe other Sinterrupter is operated suitably by means of a cam 24 drivenby an auxiliary shaft 25 preferably through a 2 to 1 reduction gearing26 and controls a con-k tact 21.

With each revolution of the shaft I4 the cornmutator 23 closes itscontact once ior eachquadrant. The cam 24 controls the-contactv21toflold 10 the circuit open during alternatefcomplete revolutions of theshaft |4. Between interruptions at the contact 2`| the commutator V23produces 'a sequence of four pulses during which the 'audible tone fromthe source 2| `:is applied to the receiver 22 through .the circuit whichhas been described. "Inthe assumed .condition of correct pointing of thereceiving device, the pulses in the acoustic `receiver '22 `are of equalintensity as represented graphically inl'iiig. 2. If' desired, thecommutator2'3 maybe replaced'by a permanent conneclt'ionwin which Acasethe acoustic response vis unmedulated. except for 4the interruptions.caused 'by `the .contact "21.

'In Lthe k.general `case where the system Il) is incorrectly .po'intedwhich Acase will' now be considlered, the radiation reaching thethermistor I5 from the 'reflector 1|| varies cyclically `during eachifevo'lu'tionofithe shaft I4. YTheheatingeifect off the radiation upon'the thermistor v`l5 will vary 'accordingly during `the cycle, resultingin a rhythmical variation ofA the temperature of lthe therni-isto'r and'a. corresponding variation ofl 'the 'instantaneous' value of v'itsresistance. Accordingly, onefoff the pulses in eachcycle in .thereceiver will` "be of greater intensity than the others, and apar-tcularrhythm Wiilbe 'introduced into the .-response, yas illustrated.graphically Yin Fig. 13 jorFig. 4, Vto give only two examples. `If thecom- .niutator 23' is inotrused, the acoustic response is 'a'toneundergoing a continual lamplitude modulation in .the intervals betweenthe interruptions caused -by 'the contact 21. Use of the commuftat'or 23to .produce four pulsesjin a group, as

.i'llustratedgtgives a rhythm correspondlngto 'fourourtime'in Lmusicalnotation, with ,the `position the accented heal". depending upon which"ample, with an error of' pointing of the device toofhigh in elevation,and t'lierhythrn of Fig. 4,

for example, with pointing to the *right of the some. Bypropey alteringthe-pointing of 'the device, La. condition 4maybereached.in which thepulses-are all-of equal intensity, as illustrated 'in "Fig. LT2,"indicatingthatv `'the pointing of the axis .""offfhe reflector |'I :ispre'cisey -in the direction 'of j fthe-incomingradiation. Thecorrerationbetween the accente'dbeat :and "the" quadrant ofmaximuin "response-maybe controlled in 'several' ways 'that 'will 'be evident `to yone skilledin Kthe art, "a 'convi '25 tiany -proportionn to `the Yradiation.reaching .the

4 some cases this may be undesirable. To obviate .this condition,` abridgecircuit may tbe 'employed iasishown in Figf, the'bxidgecomprisin'g'xed resistance arms 28 and 29, the thermistor |5 and avariable resistor or rheostat 3|).v The acoustic receiver 22 and thesource 2| are connected to 'the bridge :diagonals in conjugate relationto each other as shown. The interrupters are 4shown inthe same kdiagonalwith the receiver in Fig-5, but, lif desired, the receiver and thesource may 'be' interchanged, or the interrupters may be placed in thesame diagonal in which the source 'is shown `Vin Fig. I5.A Groundconnections 32 and 33 complete the electrical circuit through the shaftI4 to the thermistor I5 and commutator 23.

vIn the arrangement o'f Fig.. 5, when substituted Yin the 'system ofFig. l, the bridge may befbalancedby adjusting the rheos'tat 30 in theabsence o'f 'radiation or with Athe receiver .pointed in Lthe directionof 'minimum radiation. When increased radiation is received, thethermistor "f5 changes .its resistance, thereby unbalancing the bridge.and enabling current 'to flow through thelrec'eiver. 22 'whenever thecircuit is closed Vat .the interrupters. The intensity of the responseiis vsubstanelement I5.

The shaft |`4 may pass 'through'suitable openings 'and 'bearings in 'thereflector and in .the supporting structure. Means maybe lprovided as'is-well known in the art for turning `the re- -iiector and associatedequipment Lto .point the 'axis of the re'ector 'in any desireddirection. YThe thermistor I5 may be supported by means. of sufficientrigidity inthe lead `I6 or or both, or'in any other suitabIe'manner.

It will be evident that 'any suitable scanning antenna vsystem may bevsubstituted 'forgthat illustrated, the particular scanning system usedvnot lforming -an essential 'part of vthe 'present inven tion.

Furthermore it will be evident v'that 'the 'scanning system I0 together'with the commutator `23 and contacter 23 constitutes a Vparticularexample of "a lobe 'switching'arrangement Any other 'suitable lobeswitching systemmaybe .employed venientiway be'infgfbyfadjusting theangular posi of fthe rcontacter V25" on thefs'ha'ft |'4 with respect 'tothe f element 5.

"The system -c Fig. 1 Ywill `respond with pulses evenfltli'ou'g`hino.radiation fis being receivedl in instead, thev particular form usedbeing again no essential part o'f the invention.

Many other-variations ofthev 'system 'illustrated will occur to thoseskilled in this art. The .radi'ation received can be either steady or in.the -form of pulses and it may be either heterogeneous in frequency, asfor example, infra-red radiation, or substantially a 'single frequencyas in radio communication. vIf the received' radiation Aoccurs `inpulses at a 'suitable audio rate, the audio 'frequency may bedemodulated by means of Aa 'suitable receiver and 'thev audio frequencycomp'onent Afrom the receiver supplied to the circuit in place of energyfrom the lo'cal source 2|. In case the received radiation lis'unmo'dulated .the system of Fig. 'l maybe employed, or, 'alternatvely,the received radiation may be' rectied and broken up bym'ea'ns o'f lacornmutatarv and used in place of the vcurrent from the source f2'I 'o'rto control a local sourcesuch as ithesource 2| When a local 'source isthus controlled, the 'output of the `source -2| `is `modulated by' thethermistor I5 and by the' interrup'ter 21, `butinthis case thecommutator 23 is inserted in the output circuit ofthe rectifier insteadof directlyiin 'the circuit of the source 2| and receiver '22.

"It will be evident also 'that two 'different 'audio frequencies mightbe controlled'by separate commutators such as commutator 23, one iterthe azimuth correction and the other for the elevation correction. Thetwo audio frequencies might be applied to separate earphones for the twoears and separately balanced by the operator.

The radiant energy sensitive element I5 has been described as athermistor or bolometer; but it is to be understood that it issuflicient if the element l5 produces a resistance eiect that varies Yas a function of the intensity of the radiant energy striking theelement, whether the resistance variation is due to a temperature changein the element, or whether the resistance variation is caused by meansother than temperature change. The variable resistance eifect producedmay reside in the element I5 or, if desired, in a separate circuitcoupled to the element I5 in any suitable manner, as for example in astationary circuit coupled to the element I5 through slip rings. In thelatter case the element I5 may comprise a probe or antenna connected toa radio receiver, the Aantenna being preferably a quarter wavelengthhalf-dipole extending radially from the shaft I4 and lying in the focalplane 3|. In this case, the shaft is preferably modified to form acoaxial transmission line and the antenna mounted in accordance with theteachings of the abovecited application of P. H. Smith.

Wherever theV term thermistor or bolometer is used in this specificationor in the appended claims the term is intended to include any devicewhich produces a resistance effect or amplitude of response that variesas a function of the intensity of the radiant energy received at aspeciiied 1ocation.

Instead of interrupting the circuit periodically to obliterate alternategroups of pulses, other provision may be made for imparting a definitetime position in the sequence to each audible pulse. For example, therst pulse of each group may be distinguished by a tone of differentfreqency from the rest or by two tones sounding together, in which caseno silent interval is necessary. In general, any suitable means may besupplied to mark or identify acoustically a reference phase in thescanning cycle, the introduction of the silent cycle being a particularform of acoustic identification.

What is claimed ls:

1. A directionally selective receiving system for radiant energycomprising means having a reference axis, said means functioning to scancyclically over a range of directions symmetrically related to saidreference axis, said scanning means including means for producing aresponse which varies in amplitude over the scanning cycle when the saidreference axis is directed at a material angle with respect to adirection from which radiant energy is incoming, a source of audiblewaves, means to modulate the amplitude of the waves emitted from saidsource in accordance with the said variations in the response of saidscanning means, and means substantially inde pendent of duration andamplitude to provide an acoustic identification of a reference phase inthe scanning cycle.

2. A directional system comprising wave receiving means havingdirectional selectivity, means to orient said receiving means cyclicallyin a succession of directions symmetrically disposed with respect to a,given movable axis, means to generate a recurrent sequence of audiblepulses in response to waves intercepted by said receiving means inrespective portions of said cycle of orientation, said individual pulsesbeing substantially uniform in duration, and means independwhich variesover the scanning cycle when the y reference axis is directed at amaterial angle with respect to a direction from which radiant energy isincoming, a source of audible waves, means to modulate the amplitude ofthe waves emitted by said source in accordance with the variations inthe response of said scanning means, and means to suppress the emissionof said audible Waves throughout substantially the Whole of alternatescanning cycles.

4. A directional system comprising wave receiving means havingdirectional selectivity. means to orient said receiving means cyclicallyin a succession of directions symmetrically disposed with respect to agiven movable axis, means to generate a recurrent sequence of audiofrequency pulses in response to waves intercepted by said receivingmeans in respective portions of said cycle of orientation, acousticmeans to detect amplitude variations among said pulses caused by adeviation of said movable axis from the direction of propagation of saidintercepted waves and means independent of pulse duration and amp1itudefor acoustically distinguishing a reference pulse in each cycle oforientation of said receiving means, whereby a particular rhythm in thesequence of pulses may be correlated with a deviation of the saidmovable axis in a particular direction.

5. A directionally selective receiving system for radiant energycomprising means having a reference axis, said means being for scanningcyclically over a range of directions symmetrically re lated to saidreference axis, said scanning means including means for producing aresponse which varies over the scanning cycle when the reference axis isdirected at a material angle to a direction from which radiant energy isincoming, a thermistor actuated by the response of said scanning means,electrical means for generating audible waves, means controlled by saidthermistor to modulate the amplitude of the waves emitted by saidgenerating means in accordance with the variations in the response ofsaid scanning means, and means independent of duration and amplitude foracoustically distinguishing the said response at a reference phase inthe scanning cycle.

6. A directionally selective receiving system for radiant energycomprising means having a reference axis, said means being for scanningcyclically over a range of directions symmetrically related to saidreference axis, said scanning means including means for producing aresponse which varies over the scanning cycle when the referencev axisis directed at a material angle to a direction from which radiant energyis incoming, electrical means for generating audible waves, a variableresistor the resistance of which varies in accordance with the responseof said scanning means, means serially connecting said generating meansVwith said variable resistor, and a circuit interrupter included in saidserial connection and actuated by said scanning means, whereby the saidserial connection isinterrupted during substantially the whole ofalternate scanning cycles.

7. A directionally selective receiving system for radiantenergyccmprising meanshaying a refera- Veneeaxis, said means beingv forscanning cyclically over a range of directions syrnrnetrically relatedYte said v.reference axis, said scanning Vmeans in- ".cluding ymeans forproducing a response which yariesover the scanning cycle whenthereference axisisdirected .atia material angle to a direction -VfromyWlgiicla radiant energy is incoming, electrical smeans .for generatingaudible waves, electrical means-tto modulate the amplitude of Atheaudible -rwavestemitted .by said generating .means in acicordance `withthe Variations in the response o .f said scanning means, acommutatingdevicevfor .breaking up the action of .saidfgenerating means.ntoia plurality of pulses, `and means independent .nfpulseduratiQn Vandamplitude for acoustically ldistinguishing areference pulse ineachscanning J`cycle.

8. A directionally selective receiving system :for ..radiant energsrcomprising means having Aa ref- Aerenceaxis,*said means beingforscanning cycli .reallyaoyer .a .range of directions symmetricallyrelated to 'said :reference axis, said :scanninfgimeans including meansAfor intercepting--an amount-sof radiant energy which varies over the'scanning cycle when the reference axis is rdirected at a material angleto a direction from which radiant energy isincoming, a bridge circuithavingiastone arm a resistor of resistance variable as a,- function ofirradiation by radiant energy and exposed to the vincoming radiantenergy intercepted by said scanning means, said bridge circuit-beinginitially balanced with said directionally selective :receiving systemdirected to intercept minimum radiation, electrical means for generatingaudible Waves, means controlled by imbalance .of said bridge circuit,induced by radiant energy-reaching said Variable resistor tomodulatethe amplitude of the Waves emitted bysaid generating means inaccordance with the degree lof unbalance., and means independent ofduration and amplitude for aooustically distinguishing the .emitted,waves ata reference phase in the scanning cycle.

DONALD .A- QUARLES.

